Saturday, 5 January 2013

PostgreSQL cluster using DRBD and hot standby

Cluster Configuration:

First install all the necessary packages:
yum install gfs2-utils cman fence-virtd-checkpoint lvm2-cluster perl-Net-Telnet rgmanager device-mapper-multipath ipvsadm piranha luci modcluster cluster-snmp ricci
yum groupinstall "High Availability"
yum install postgresql-server
chkconfig --level 123456 ricci on
chkconfig --level 123456 luci on
chkconfig --level 123456 cman on
chkconfig --level 123456 iptables off
chkconfig --level 123456 ip6tables off
chkconfig postgresql on
chkconfig cman on
chkconfig rgmanager on
Now edit the cluster configuration file:
vi vi /etc/cluster/cluster.conf
Make it look like this:
<?xml version="1.0"?>
<cluster config_version="7" name="pgcluster">
<clusternode name="" votes="1" nodeid="1">
<clusternode name="" votes="1" nodeid="2">
<failoverdomain name="PGSQL" nofailback="0" ordered="0" restricted="0">
<failoverdomainnode name=""/>
<failoverdomainnode name=""/>
<ip address="" monitor_link="on" sleeptime="10"/>
<postgres-8 config_file="/var/lib/pgsql/data/postgresql.conf" name="pgsql" shutdown_wait="5" />
<service autostart="1" exclusive="0" domain="PGSQL" name="pgsql" recovery="relocate">
<drbd name="drdb-postgres" resource="r0">
<fs device="/dev/drbd0" fsid="6202" fstype="ext3" mountpoint="/var/lib/pgsql" name="pgsql" options="noatime"/>
<ip ref=""/>
<postgres-8 ref="pgsql"/>
<cman expected_votes="1" two_node="1"/>
<fence_daemon clean_start="1" post_fail_delay="0" post_join_delay="3"/>

DRDB Configuration:

Install the necessary files:
yum install gcc flex make libxslt rpm-build redhat-rpm-config kernel-devel
You need to download and install DRBD manually
 the following commands will generate DRBD RPM packages:
tar -xvf *.tar.gz
mkdir -p /root/rpmbuild/SOURCES/
cp drbd*.tar.gz /root/rpmbuild/SOURCES/
cd drbd-8.4.1
./configure --with-rgmanager --enable-spec --with-km
make tgz
rpmbuild --bb drbd.spec --without xen --without heartbeat --without udev --without pacemaker --with rgmanager
rpmbuild --bb drbd-kernel.spec
rpmbuild --bb drbd-km.spec
Now install the newly created packages:
cd /root/rpmbuild/RPMS/x86_64
rpm -i drbd-utils-8.4.1-1.el6.x86_64.rpm drbd-bash-completion-8.4.1-1.el6.x86_64.rpm drbd-8.4.1-1.el6.x86_64.rpm drbd-rgmanager-8.4.1-1.el6.x86_64.rpm drbd-km-2.6.32_279.14.1.el6.x86_64-8.4.1-1.el6.x86_64.rpm
Add your nodes IP addresses to the hosts file on both machines:
vi /etc/hosts RHPG1 RHPG2
Create a DRBD configuration file:
vi /etc/drbd.d/r0.res
resource r0 {
   device /dev/drbd0;
   meta-disk internal;
   on RHPG1 {
      disk /dev/sdb1;
   on RHPG2 {
      disk /dev/sdb1;
Create the partion /dev/sdb1 but do not format it:
fdisk /dev/sdb
Run on both machines:
drbdadm create-md r0
modprobe drbd
drbdadm up r0
Run on one of the machines to create the file system:
drbdadm -- --overwrite-data-of-peer primary r0
Check the sync status on any of the hosts with:
service drbd status
Create the file system on /dev/drbd0
mkfs.ext3 /dev/drbd0
and move over the PostgreSQL data
mkdir /tmp/pgdata
mount /dev/drbd0 /tmp/pgdata
cp -r /var/lib/pgsql /tmp/pgdata
Wait until the data is synced over the two hosts check the status with:
service drbd status
Unmount the drbd device:
umount /dev/drbd0
and then, on both hosts do:
rm -rf /var/lib/pgsql/*
Restart the drbd service
service drbd restart
the status from:
service drbd status
should show that both hosts are in secondary:
0:r0 Connected Secondary/Secondary UpToDate/UpToDate C
And ready to be managed by rgmanager.

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